Control device for medical catheters

ABSTRACT

A control mechanism comprises an elongate handle  10  having an external thread  12  and a barrel  20  with internally projecting pins  21  threaded over handle  10 . Rotation of barrel  20  causes handle  10  to move back and forth along its longitudinal axis to retract and advance a catheter sheath to which handle  10  is coupled, thereby enabling an implant to be deployed by the catheter. Rotation movement of barrel  20  and longitudinal movement of handle  10  can be disassociated to enable speedy retraction or advancement of the catheter sheath.

FIELD OF THE INVENTION

The present disclosure relates to an improved mechanism for controllingmedical catheters and more particularly those catheters which are usedto deliver implants to particular sites within a patient's body, such ascardiovascular stents. The system has applications in a wide range ofcatheter or laparoscopic surgery and is of particular value indelivering larger implants, such as stent grafts, within arteries.

BACKGROUND OF THE INVENTION

Catheter delivery systems usually comprise a sheath at whose tip iscontained the device to be implanted. The device is usually highlycompressed, particularly in diameter, and the device is released bydrawing the sheath back, allowing the device to emerge from its tip. Alldesigns feature a structure which provides a reaction force for thedevice so that it maintains its position while the sheath is beingwithdrawn.

A simple example of this type of delivery system is provided with theTalent™ stent-graft manufactured by Medtronic, Inc. The system sufferstwo principal draw-backs. The first is that the highly compressedimplant pushes against the wall of the sheath with such force thatwithdrawing the sheath also requires a considerable force. A second(allied) problem is that providing the necessary force to deploy thestent-graft can be difficult for the medical practitioner to achievewith accuracy or control, allowing the implant to be deployed tooquickly and, potentially, displaced from its intended landing site.

An improved system has been incorporated into the delivery systemsupplied with the AneuRx™ stent-graft, also manufactured by Medtronic.In this system, a barrel-shaped component of the handle of the deliverysystem is rotated and acts on a lead-screw to withdraw the sheath withboth mechanical advantage and precision.

Additional complexity is added in this system because the sheathstretches significantly while it is being withdrawn. When the medicalpractitioner's hand is being repositioned on the barrel of the handle,the barrel is free to rotate and is prone to spin back as the sheathsprings back to its original length. The AneuRx™ system thereforeemploys a conventional ratchet mechanism on the rotating barrel toprevent this elastic recoil.

Introduction of the ratchet incurs a further complexity. When thedelivery catheter is being withdrawn from the patient, it is highlydesirable that the sheath be slid back into its original position tocover the remaining internal components of the delivery system so thatthey do not inflict any trauma onto the viscera of the patient. For thispurpose, the AneuRx system employs a separate control to override theratchet and allow the barrel to be rotated in the opposite sense toallow the sheath to be returned to its starting position.

SUMMARY OF THE INVENTION

The present invention performs similar functions to the AneuRx systembut employs fewer components, allowing it to be fabricated more cheaply,operated more simply and for the mechanism to have greater reliability.

According to a first aspect of the present invention, there is provideda control mechanism for retraction and advancement of a sheath at theend of a delivery catheter, comprising a first part which is able tomove back and forth along a longitudinal axis, said first part beingassociated with the catheter sheath so that movement of said first partin one direction along said axis causes retraction of the sheath andmovement in the opposite direction causes advancement of the sheath, asecond part which can be rotated about a rotation axis, movement of saidfirst and second parts being associated whereby rotation of said secondpart causes said first part to move along said longitudinal axis toretract or advance the catheter sheath depending on the direction ofsaid rotation, wherein movement of said first and second parts can bedisassociated to allow movement of said first part to advance the sheathwithout corresponding rotation of said second part.

The invention preferably employs a rotatable barrel on the handle of thedelivery system, said barrel being connected permanently to a tubularsheath which is used to contain the implant during insertion into thepatient. The rotatable barrel has a first threaded feature on at leastone of its cylindrical surfaces which engages a second threaded featureon the handle of the delivery system so that when rotated, the barrelmoves axially along the said handle. An alternative embodiment can beconstructed in which the rotatable barrel is held axially captive andits threaded feature engages a second threaded feature on an additionalcomponent which is itself connected permanently to the sheath and movesaxially along the handle as the barrel is rotated, moving the sheathinto or out of the handle.

A preferred feature of the present invention is a modification to thefirst or second threaded component. The modification allows the diameterof the threaded component to be increased if it is an outer thread, orto be decreased if it is an internal thread, beyond a point where thefirst threaded component no longer engages the second threadedcomponent. The modification allows the rotatable barrel to have twomodes of operation: the first operating mode occurs when the first andsecond threaded components are engaged, the barrel is rotated andoperates the lead screw to provide mechanical advantage and a slowcontrolled release. The second operating mode occurs when the first andsecond threaded components have been adjusted so that they cannot engageand the rotatable barrel can be slid axially, without mechanicaladvantage but at higher speed. The first operating mode is optimum forreleasing the implant while the second operating mode is more suitablefor returning the sheath to its starting position, or for deploying asecond, less critical component of the implant.

An improvement to this basic system includes provision for the diameterof at least one threaded component to be adjusted by at least onefeature on the thread or handle. In this case, the threaded parts can bedisengaged when the said feature or features are reached at a point orpoints along the thread. Thus the lead-screw action can be engineered tobe effective over a defined length or lengths while permitting thesecond mode of operation over the remaining length or lengths.

A further improvement in the basic system can be achieved if themodified threaded component is stable in both the engaged or disengagedstates. This allows the mechanism to employ the mechanical advantage ofthe lead-screw, but once disengaged to return over the threaded part asa simple sliding movement. This feature allows the rapid return of thesheath to the starting position.

An additional improvement to at least one of the threaded componentsinvolves introducing discontinuities into the thread so that tension inthe sheath will not encourage the rotatable barrel to spin when it isreleased. Various discontinuous features can be included ranging betweena random roughening of the profile of the thread which increasesfriction between the first and second threaded components to a‘staircase’ type feature in the thread so that it has alternatingstationary and advancing components along its length. It will beunderstood that recoil in the sheath will cause the barrel to returnalong the length of an advancing part of the thread but to remainstationary when a stationary component of the thread has been reached.

In all cases, benefit can be derived from the use of multiple or‘multi-start’ threads in this mechanism.

In a practical embodiment of the invention, the handle of the cathetersystem is threaded over part of its surface with a multi-start thread. Arotatable barrel with a smooth inner surface is free to slide over thethreaded handle. The barrel is provided with a number of shortcylindrical pins which are radially arranged to pass through the wall ofthe barrel. Preferably, where a multi-start thread is employed, at leastone radially arranged pin is employed to engage with each separatethread. The pins can slide in the wall of the barrel and their length isarranged such that when in a first position, they project maximally intothe barrel and the pins engage the thread of the handle. Thus the pinsform the first threaded component referred to above and the threadedhandle comprises the second threaded component. In a second position,the pins can be pushed outwards through the wall of the barrel so thatthey no longer engage the thread of the handle, allowing the barrel tomove freely over the threaded handle.

The fit of the pins in the wall of the barrel and the selection ofmaterials can be made such that the pins can be held firmly in eitherthe said first or the said second positions. Practical materials for thebarrel include polyester and the pins can be suitably manufactured from316 stainless steel.

Conveniently, the pins can be moved from the said first position to thesaid second position by decreasing the depth of the thread cut into thehandle or by providing a raised component over which the pins are madeto pass. Advantageously, the diameter of the pins is increased at oneend, said end lying inside the rotatable barrel. This feature preventsthe pin from falling out of the barrel, while the length of the pin issuch that the body of the handle passing through the rotatable barrelwill prevent the pin from falling through the wall of the barrel intothe handle.

Typically, the handle has a diameter of 10 to 40 mm although systemswith handles as small as 3 mm in diameter and as large as 150 mm indiameter could usefully be made. Considering a typical system with ahandle of 25 mm diameter, the thread depth is conveniently 2 mm±+1 mmwith a pitch of 20 mm±10 mm per turn. The rotatable barrel isconveniently between 30 mm and 100 mm long while its wall thickness is 4mm±2 mm. The internal diameter of the rotatable barrel is ideally lessthan 1 mm larger than the outer diameter of the threaded part of thehandle. The pins which comprise the first threaded component are 2 mm±1mm in diameter and have an overall length which is approximately the sumof the wall thickness of the barrel plus the depth of the thread plushalf the clearance between the internal diameter of the rotatable barreland the outer diameter of the threaded part of the handle. Those skilledin the art will appreciate that the many combinations of dimensions canbe chosen which will provide a functioning system and that finalselection will depend upon ease and reproducibility of manufacture aswell as the ergonomics of the system for the user. When designing largeror smaller systems, the basic dimensions for the 25 mm system should bescaled as appropriate and then adjusted for ergonomics and ease ofmanufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of preferred embodiments of the present invention will now bedescribed with reference to the drawings, in which:—

FIG. 1 shows a perspective view of a control mechanism in accordancewith the present invention;

FIG. 2A shows a cross-sectional view of the control mechanism at FIG. 1;

FIG. 2B shows a perspective view of the barrel of FIG. 2A shownseparately from the rest of the components;

FIG. 3A is a cross-sectional view of a control mechanism in accordancewith the invention in a different position to that shown in FIG. 2A;

FIG. 3B is a cross-sectional view of a control mechanism in accordancewith the invention in a different position to that shown in FIGS. 2A and3A;

FIG. 4A is a perspective view of the barrel of the control mechanism ofFIG. 4B shown separately from the rest of the components; and

FIG. 4B is a cross-sectional view of a control mechanism in accordancewith the invention shown in a different position to that of FIGS. 2A, 3Aand 3B.

DETAILED DESCRIPTION OF PREFERRED VERSIONS OF THE INVENTION

The control mechanism comprises a handle (10) which is an elongateelement with a central bore (14) through which delivery catheter (30)can pass. The outside surface of handle (10) has thread (12) with aplurality of steps (13) therein and a stop (11) at one end of handle(10).

Barrel (20) has four pins (21) projecting from its inner surface, pins(21) engaging with thread (12) to enable barrel (20) to be threadedaxially over the external surface of handle (10).

The external surface of barrel (20) has a hand grip (22) to enable theuser to grip barrel (20) and rotate it about handle (10).

Pins (21) are mounted in four holes (not shown) in barrel (20) and areable to move radially from a position of maximum projection into thecentre of barrel (20) to a position of radial retraction and minimalprojection into the centre of barrel (20). This enables pins (21) toengage and disengage with thread (12) as will be described below.

Catheter delivery tube (40) is disposed in the bore of handle (10) atthe end distal to stop (11) and positioned coaxially with handle bore(14) such that catheter (30) can be threaded through catheter deliverytube (40) and bore (14) to emerge as shown in FIG. 1.

FIGS. 2A and 2B, 3A and 3B and 4A and 4B show pins (21) in states ofincreasing disengagement from thread (12), that is from a state in whichpins (21) project radially into the centre of barrel (20) in FIGS. 2Aand 2B to a state in which pins (21) are retracted into barrel (20) andthereby disengaged from thread (12) (FIGS. 4A and 4B) with FIGS. 3A and313 showing state of partial disengagement.

In use, barrel (20) is rotated anticlockwise about the longitudinal axisof handle (10) with pins (21) engaging in thread (12) as shown in FIG.2A. This rotational movement causes pins (21) to move down thread (12)away from stop (11), thereby causing longitudinal movement of barrel(20) away from stop (11) down thread (12).

Coupling between barrel (20) and the distal end of catheter (30) (notshown) causes the sheath at said distal end to retract, thereby baringthe end of catheter (30) and delivering the device to be implanted fromcatheter (30).

If the user releases barrel (20) then elastic recoil of the cathetersheath will cause rotation of barrel (20) in a clockwise sense. However,pins (21) will quickly become lodged in steps (13), thereby preventingfurther clockwise rotation of barrel (20) and preventing advancement ofthe catheter sheath.

As barrel (20) is rotated further, pins (21) reach the end of thread(12) distal from stop (11). Pins (21) then ride up a ramp (not shown) atthe end of thread (12) which urges pins (21) radially outwardly toretract into barrel (20). FIG. 3A shows a single pin (21) beginning todisengage and FIG. 3B shows said pin almost fully disengaged. When pins(21) are fully disengaged from thread (11), handle (20) can be movedaxially towards stop (11) without the need for rotation of barrel (20).This thereby allows advancement of the catheter sheath to re-cover theend of catheter (30).

In an alternative embodiment, continuing longitudinal movement of barrel(20) away from stop (11) without the need for continuing anti-clockwiserotation of barrel (20) is possible once pins (21) have reached the endof thread (12). The user can thereby withdraw the catheter sheathcompletely by fast longitudinal separation of barrel (20) and handle(10) with the more controlled rotational separation being reserved forthe first part of the separation.

Once the implant has been delivered from the catheter, the user canadvance the catheter sheath by moving barrel (20) towards handle (10)longitudinally without the need for rotational movement of barrel (20).As pins (21) reach the end of handle (10) distal from stop (11) a rampon handle (10) may be provided to urge pins (21) to retract into barrel(20) and allow continuing longitudinal movement without the need forrotation of barrel (20) with respect to handle (10).

1. A catheter sheath with a sheath control mechanism for retraction andadvancement of the sheath, the control mechanism having: a. a first partwhich is able to move back and forth along a longitudinal axis, thefirst part being associated with the catheter sheath so that movement ofthe first part in one direction along the axis causes retraction of thesheath and movement in the opposite direction causes advancement of thesheath, b. a second part which can be rotated about a rotation axis,wherein: (1) the movement of the first and second parts is associated bya thread disposed on one of the first and second parts, the other of thefirst and second parts having a lug which is able to move into and outof the thread, whereby rotation of the second part causes the first partto move along a longitudinal axis to retract or advance the cathetersheath depending on the direction of the rotation, (2) the lug isdisengageable to disassociate the movement of the first and secondparts, thereby allowing movement of the first part to advance the sheathwithout corresponding rotation of the second part, and (3) the one ofthe first and second parts having the thread disposed thereon has aramp, up which the lug moves on rotation of the second part, the rampurging the lug out of the thread to thereby disengage the lug from thethread.
 2. The control mechanism of claim 1, wherein the first part isan elongate element and the second part is a sleeve which fits over theelongate element.
 3. The control mechanism of claim 1, wherein thelongitudinal movement of the first part beyond an end of the threaddistal to the catheter sheath causes disassociation of the movement ofthe first and second parts.
 4. The control mechanism of claim 1, whereinthe ramp is disposed at an end of the thread.
 5. The control mechanismof claim 1, additionally comprising means for preventing free rotationof the second part in such a manner as to allow advancement of thesheath.
 6. The control mechanism of claim 5, wherein the means forpreventing comprises an abutment surface in the thread.
 7. A cathetersheath with a sheath control mechanism for retraction and advancement ofthe sheath, the control mechanism having: a. an elongate element whichis able to move back and forth along a longitudinal axis, the elongateelement being associated with the catheter sheath so that movement ofthe elongate element in one direction along the axis causes retractionof the sheath and movement in the opposite direction causes advancementof the sheath, b. a sleeve which can be rotated about a rotation axis,wherein: (1) the elongate element and sleeve are associated by a threadand a member engaging the thread, whereby rotation of the sleeve causesthe elongate element to move along the longitudinal axis to retract oradvance the catheter sheath depending on the direction of the rotation,(2) the thread has steps indented therein, the steps: (a) being spacedalong the thread, and (b) each extending at least partially in alongitudinal direction,  wherein the member restrains relative rotationof the elongate element and sleeve in at least one of the clockwise andcounterclockwise directions if the member is urged into one of thesteps, and (3) the thread can be disengaged from the member to allowmovement of the elongate element to advance the sheath withoutcorresponding rotation of the sleeve, and (4) the thread has a ramp, upwhich the member moves upon relative rotation of the sleeve and elongateelement, the ramp urging the member out of the thread in order todisengage the member from the thread.
 8. The control mechanism of claim7 wherein the member is movable in an at least partially radialdirection to disengage from the thread.
 9. The control mechanism ofclaim 7 wherein each step is bounded by opposing sides spacedcircumferentially along the thread, one of the sides being ramped suchthat when the member is within one of the steps, relative rotation ofthe elongate element and sleeve in one of the clockwise andcounterclockwise directions drives the member up the ramp of the step.10. The control mechanism of claim 7 wherein the ramp is disposed at anend of the thread.
 11. The control mechanism of claim 1 wherein thethread has steps depressed therein, the steps: a. being spaced along thethread, and b. each extending at least partially in a longitudinaldirection, wherein the lug restrains relative rotation of the first andsecond parts in at least one of the clockwise and counterclockwisedirections if the lug is urged into one of the steps.
 12. The controlmechanism of claim 11 wherein each step is bounded by opposing sidesspaced circumferentially along the thread, one of the sides being rampedsuch that when the lug is within one of the steps, relative rotation ofthe elongate element and sleeve in one of the clockwise andcounterclockwise directions drives the lug up the ramp of the step. 13.A catheter sheath with a sheath control mechanism for retraction andadvancement of the sheath, the control mechanism having: a. a first partwhich is able to move back and forth along a longitudinal axis, thefirst part being associated with the catheter sheath so that movement ofthe first part in one direction along the axis causes retraction of thesheath and movement of the first part in the opposite direction alongthe axis causes advancement of the sheath, b. a second part which can berotated about a rotation axis, wherein: (1) one of the first and secondparts bears: (a) threading extending along a length parallel to thelongitudinal axis, and (b) a ramp with height varying in a radialdirection, (2) the other of the first and second parts bears a memberwhich is movable in an at least partially radial direction to engage anddisengage the threading, and (3) upon relative rotation of the first andsecond parts, the ramp urges the member radially out of the thread inorder to disengage the member from the thread, whereby: i. the membercan engage the threading to rotatably associate the first and secondparts, whereby rotation of the second part causes the first part to movealong the longitudinal axis, and ii. the member can disengage thethreading to disassociate the first and second parts, whereby at leastone of the first and second parts can move longitudinally with respectto the other part without relative rotation between the parts.
 14. Thecontrol mechanism of claim 13 wherein the ramp is disposed at an end ofthe thread.
 15. The control mechanism of claim 13 wherein the thread hassteps indented therein, the steps: a. being spaced circumferentiallyalong the thread, and b. each extending at least partially in alongitudinal direction, wherein the member restrains relative rotationof the first and second parts in at least one of the clockwise andcounterclockwise directions when the member rests within one of thesteps.
 16. The control mechanism of claim 15 wherein each step isbounded by opposing sides spaced circumferentially along the thread, oneof the sides being ramped such that when the member is within one of thesteps, relative rotation of the elongate element and sleeve in one ofthe clockwise and counterclockwise directions drives the member up theramp of the step.